430 WESLEY E. COE, 



progress the few short fibers remaining, so that it can no longer be 

 seen. The projection now constricts off from the rest of the cell to 

 form the first polar body. This process is completed in less than 

 six minutes after the formation of the spindle, or in about twenty to 

 twenty-six minutes after being placed in the water, provided the egg 

 is fertilized at any time during the first fifteen minutes. The aster 

 remaining in the egg loses its distinctness, and is soon replaced by 

 two smaller asters. These lie obliquely to the surface, but soon 

 assume a radial position corresponding to that occupied by the first 

 polar spindle. A second, and smaller, polar body is formed in like 

 manner to the first, and about eight minutes later. The egg is per- 

 ceptibly flattened in the region of the polar bodies. 



The aster of the second polar spindle remaining in the egg now 

 loses its distinctness and in its centre, or slightly to one side, the 

 vesicles which are to form the egg-nucleus make their appearance ^). 

 As these vesicles fuse together the radiations about them are gradually 

 absorbed, but only very slowly, so that ten or twelve minutes elapse 

 after the separation of the second polar body before the last traces 

 of the radiations have disappeared. During all this time the egg- 

 nucleus changes its position but slightly, although it continues to 

 increase in size. 



The spermatozoon may enter the egg at any point, but in the 

 great majority of cases this is somewhere on that side of the cell 

 which lies opposite the region of the polar spindle. In eggs fertilized 

 while the germinal vesicle is still intact, this rule holds good; for 

 the position which the future polar spindle is to occupy is already 

 roughly predetermined, as was noted above ; so that in such eggs the 

 spermatozoa usually enter in the region farthest from the eccen- 

 trically placed germinal vesicle. 



It is usually ten to fifteen minutes after the entrance of the 

 spermatozoon into the egg before its presence can be detected there. 

 A series of delicate radiations then appear, sometimes as a single 

 aster, more often as two. If but one, this soon divides, although the 

 two asters usually remain in close proximity. In their immediate 

 vicinity the sperm-nucleus can now be seen. Most commonly this 

 lies on the side of the asters farthest from the centre of the egg, 

 though this is not universally the case. The asters increase rapidly 



1) The behavior of the chromosomes cannot be followed in the 

 living egg. 



